The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Currently the Global Positioning System (GPS) IIF transmits exactly 3 binary phase shift key (BPSK) codes using Interplex modulation such that the transmitted signal has a constant power. GPS III needs to transmit 2 additional BPSK codes. However, it is strongly desired that the transmitted signal still should have a constant power. Hence, these two additional codes need to be combined with the 3 original BPSK codes via some intermediate code combining technique, then modulated by the Interplex method such that the transmitted signal still maintains a constant power.
There are no satisfactory existing solutions to the problem of combining the 2 additional BPSK codes transmitted by GPS III and the 3 BPSK codes transmitted by GPS IIF. One attempt to overcome this challenge has involved the use of Interlace combining followed with Interplex phase modulation. However, the existing Interlace combining technique requires the use of a uniform random number generator. The optimality of the Interlace combining technique depends on the authenticity of the uniform random number generator (i.e., how uniformly distributed are the random numbers generated by it within a short duration) and its authenticity period (i.e., the duration it takes to achieve that uniform distribution). If these are not met, the backward compatibility requirement (the most foremost requirement) of GPS III in terms of existing shortest receiver integration time cannot be met adequately and the combined transmitted code will not be fully compatible with the existing GPS receivers in the world.